The research described in this application is designed to examine the neuronal circuitry and neurotransmitters which are responsible for the state-dependent modulation of trigeminal motoneuron membrane potential activity. Interdisciplinary electrophysiological and iontophoretic studies are proposed, each of which relates to and complements the others. These studies, which are organized within the framework of an examination of the paradoxical phenomenon of "reticular response-reversal", entail a determination of the state-dependent activity of and interrelationships between the nucleus pontis oralis, the nucleus reticularis gigantocellularis and the trigeminal motor nucleus. The proposed studies should (1) clarify a number of the specific pathways and synaptic processes that are involved in the modulation of brainstem motoneuron membrane potential activity during sleep and wakefulness, (2) generate a normative fund of information relating to the neurotransmitters underlying various patterns of postsynaptic inhibition during active sleep, and (3) provide a new experimental paradigm for studying the neurotransmitters mediating behavioral activities from an intracellular perspective utilizing iontophoretic techniques in the chronic, unanesthetized, normally respiring animals.